Gabe Mirkin, M.D.
When I was racing, I thought that the runner who runs the most training miles is the best. I didn't become a great runner, I became an expert on injuries.
The faster you run in practice, the faster you can run in races, but every time you run fast, your muscle are damaged and feel sore and it takes a couple of days to recover. If you try to run very fast when your muscles are sore, you'll tear them and won't be able to run at all. Each day of running fast should be followed by a couple of days in which you run at a slower pace. That's why competitive runners run very fast two or three times a week and longer once. The rest of the time, they run more slowly to allow their muscles to recover, so they can be torn again by their hard runs.